Contact structure for an electro-luminescent device



May 31, 1966 I 1. E. BUCK, JR 3,254,254

CONTACT STRUCTURE FOR AN ELECTROLUMINESCENT DEVICE Filed May 17, 1963 2Sheets-Sheet l 36 I8 2226 34 3 O 44 32 28 I8 22 38 IO yt l FIG. 7.

INVENTOR. IVAN E. BUCK ,JR

May 31, 1966 I. E. BUCK, JR

CONTACT STRUCTURE FOR AN ELECTROLUMINESCENT DEVICE 2 Sheets-Sheet 2Filed May 17, 1963 FIG. 9.

FIG. 8.

INVENTOR.

IVAN E. BUCK,JR.

FIG. I2.

United States Patent 3,254,254 CONTACT STRUCTURE FOR AN ELECTRO-LUMINESCENT DEVICE Ivan E. Buck, Jr., East Orange, N.J'., assignor toWestinghouse Electric Corporation, Pittsburgh, Pa., 21 corporation ofPennsylvania Filed May 17, 1963, Ser. No. 281,314 9 Claims. (Cl.313-108) This invention relates to electroluminescent lamps and, moreparticularly, to improved contact assemblies for such lamps and themanufacture thereof.

As is known, an electroluminescent lamp comprises a layer of dielectricmaterial containing an electroluminescent phosphor sandwiched between apair of electrodes. In the usual case, one electrode is opaque andcovered with a light-colored enamel or the like, while the otherelectrode is light-transmitting. Covering the light-transmittingelectrode is a layer of glass or other similar protective material. Uponthe establishment of a suitable electrical potential across theelectrodes, the phosphor will luminesce and give off light through thelight-transmitting electrode and the protective layer.

One of the problems encountered in making such lamps resides in thedifficulty of providing a suitable electrical contact for thelight-transmitting electrode which overlies the phosphor-bearingdielectric layer. The generally accepted procedure for establishment ofcontact to this electrode is to have a small area of-the electrodeuncovered by the protective layer of glass. At most, a layer of burnishsilver may be fired in place in this open area to establish a bettersurface for pres sure or soldered leads.

The phosphor-dielectric layer is the most easily at tacked layer in thelamp and, since it is adjacent the contact area in prior art assemblies,this location is weak, makes the connection of a lead to the upperelectrode difiicult without damaging the phosphor layer, and causes mostof the lamp failures. This is especially true in the case of highhumidity where lamp failure generally occurs rapidly.

As an overall object, the present invention provides an improvedelectroluminescent lamp structure which overcomes the above and otherdisadvantages of prior art lamps. Y I,

Another and more specific object of the invention is to provide animproved contact assembly for the lighttransmitting electrode of anelectroluminescent lamp, which assembly will prevent damage and failureof the lamp at the contact area due to humidity and other factors.

In accordance with the invention, the improved contact assemblycomprises a bus bar having a first portion which contacts the upperlight-transmitting electrode and which is sealed into the lamp structureduring the manufacture thereof, and a second portion which is exposed bymeans of an opening in the glass protective cover. Preferably, aninsulating layer of glass is placed under the phosphor glass layer inthe area covered by the bus bar to reinforce it and thus preventbreakageof the seal when a lead is attached to the contact.

In the manufacture of the lamp assembly, a reinforcing layer of glass orthe like is initially deposited on thelower or base electrode in thearea of the contact. Thereafter, the phosphor-bearing layer andlight-transmitting front electrode are formed and an opening is providedtherein above the aforementioned glass-reinforcing layer. This openingis then filled with a body of glass or other insulating and reinforcingmaterial which projects above the upper surface of the front electrode,and a bus bar of burnish silver or the like is then applied over aregion such that it has a first portion which covers the aforesaid bodyof insulating material and a second portion which contacts the frontelectrode. Finally, a protective layer of glass or other similarmaterial is applied to the entirety of the lamp structure except for theportion of the bus bar which is above the opening in the upper electrodeand the dielectric phosphor layer. In one embodiment of the invention,the final protective glass layer is applied in one coat; whereas inanother embodiment it is applied in two coats. In both cases, however,the result is the same, namely, a contact assembly which is sealed intoand comprises an integral part of the lamp and is also reinforcedagainst mechanical and electrical breakdown.

The foregoing and other objects and features of the invention willbecome apparent from the following detailed description taken inconnection with the accompanying drawings which form a part of thisspecification, and in which:

FIGURE 1 is a perspective view of an electro-luminescent deviceincorporating the improved contact assembly of the invention;

FIG. 2 is an enlarged sectional view taken along line II-II of FIG. 1;

FIG. 3 is a fragmentary top view of the left-hand corner of the lamp ofFIG. 1, showing the lower electrode with a base coat of reinforcingglass over it at the contact area and a phosphor glass layer appliedthereover as the first step in the manufacture of the electroluminescentlamp of the invention;

FIGS. 4l0 show successive phase or steps in the manufacture of the lampof FIGS. 1 and 2;

FIG. 11 is a cross-sectional view, similar to that of FIG. 2, of analternative embodiment of the invention; and

FIG. 12 is a fragmentary top -view of the alternative embodiment shownin FIG. 11.

EMBODIMENT I Referring now to the drawings, and particularly to FIGS. 1and 2, the lamp shown is designated generally by the reference numeral10 and includes a lower or base electrode 11 comprising a substrate ofstainless steel or the like coated with a white porcelain enamel baselayer 12. At one corner of the electrode 11, over which the contact ispositioned, is a reinforcing localized layer 14 of an insulating glasswhich fires at the same temperature as the white porcelain enamel 12.Deposited over the enameled electrode 11 as well as the glassreinforcing layer 14 is a phosphor-containing layer 16 of glass, whileabove the layer 16 is a layer of light-transmitting conductive materialsuch as tin oxide that serves as the upper or front electrode 18. Thearrangement of these components 'is such that when a suitable electricalpotential is established between electrodes 11 and 18, the phosphorembedded in layer 16 will luminesce to give off light which passesthrough the front electrode 18.

Provided in the phosphor-dielectric layer 16 and the front electrode 18is an uncoated area or opening 20 (see FIG. 2) which lies above thereinforcing layer 14. After the layer 16 and electrode 18 are appliedand the opening 20 formed, a first layer 22 of a suitable glassprotective enamel is applied over the entire surface of the electhefirst glass protective layer 22 is a second glass protective layer 38which extends down over the edges of the assembly to provide anoverlapping lip 40 that is bonded to the base electrode 11 and seals offthe laminated cell structure from the atmosphere. An opening 44 isprovided in the final glass coat 38 directly above the raised portion 32of the bus-bar 30. This raised portion is thus exposed and serves as oneof the lamp contacts.

As shown in FIG. 1, electrical leads 46 and 48 connect the baseelectrode 11 and the bus-bar 30 to an energizing voltage source throughinput terminals 50 and 52. The leads may be connected to the aforesaidbase electrode and bus-bar by soldering or pressure techniques. Sincethe front electrode 18 is completely covered or encased, it is notexposed and vulnerable to attack by water vapor or other impuritiesFurthermore, the support provided by the glass layer 22 and the lowerreinforcing glass layer 14 in the contact area assures that the bus-bar30 will not break away from the glass protective seals when connectionis made with the front contact by soldering or pressure techniques. Thisconstruction also provides additional protection against electricalbreak-down in this critical area.

FABRICATION The manufacture of the lamp 110 is illustrated instepby-step fashion in FIGS. 310. With reference, first, to FIG. 3, themetal base electrode 11 coated with porcelain enamel 12 is initiallycoated at one corner with the glass reinforcing layer 14 over apredetermined rectangular region, the outline of which is defined by thebroken line 54. Such porcelain enamels are well known and it isdeposited by spraying the upper face of the electrode 11 to form a layerabout 4 to 12 mils thick. Thereafter, the area which will be under thebus-bar 30 is reinforced by the localized application of a suitableinsulating glass 14 which fires at the same temperature as the whiteporcelain enamel. After drying, the electrode 11 is fired at atemperature to fuse the coatings. As an example, the enamel may be amaterial commercially available as Pemco Neowhite #44, in which case theassembly is fired at 800 C. for five minutes.

After the application of the reinforcing glass layer 14 and firing inthe manner described above, a layer 16 of admixed phosphor and glassfrit is deposited over the entire face of the metal base 11. The layer16 is the top layer as viewed in FIG. 3 and has its lower left-handcorner broken away to expose the glass reinforcing layer 14 andfacilitate the illustration of the invention. Then a rectangular area iscleared of the glass-phosphor layer 16 to provide an opening and exposethe glass reinforcing layer 14. The layer 16 may be deposited bysettling, spraying or screen processing techniques in a manner such thata margin of about one-eighth inch remains around its edges to expose theunderlying edges of the enamel layer 12 and reinforcing glass layer 14.After drying, the assembly is again fired.

As a specific example of a suitable glass-phosphor mixture, about 70'parts by weight of a glass frit having a lower firing temperature thanthat of the enamel layer 12 is mixed with parts by weight of ZnSzCUelectroluminescent phosphor and a suitable vehicle such as 30 parts byweight of Du Pont K595 Squeegee Oil. This mixture is then screenedthrough a 163 mesh nylon onto the substrate and fired at 620 C. for fiveminutes. The glass frit may be of the type disclosed in U.S. Patent No.3,005,722 to N. F. Cerulli. The thickness of this layer may vary fromone-half mil to several mils.

At the conclusion of the firing operation of the glassphosphor layer 16,it is sprayed with tin chloride (SnCl while at a temperature of about550 C. to provide the conductive light-transmitting or front electrode18 (FIG. 4). This front electrode is then isolated from the baseelectrode 11 by a light sandblasting operation to provide a clear marginalong the edges.

As shown in FIG. 5, the rectangular opening 20 is then cleared of frontelectrode 18 to again expose the lower glass reinforcing layer 14. Thefirst layer 22.of powdered glass protective enamel is then applied overthe entire face of the assembly, as shown in FIG. 6, by the methodsdescribed in connection with the application of the phosphor-bearingglass layer 16. After the protective glass layer 22 has dried, tworelatively small areas are cleared to form the rectangular apertures 26and 28 and expose the electrode 18, as shown in FIG. 7. This layer isthen fired to form a fused coating. Any suitable glass having a lowerfiring temperature than that of the glass frit employed in making theglass-phosphor layer 16 can be used as this cover coat.

The bus bar 30 (FIG. 8) of burnish silver is then applied by screeningor painting over an area such that it spans the apertures 26 and 28 inlayer 22 and the opening 20 which has been filled by a plug of glassthat comprises part of the layer 22. As will be noted in FIG. 2, thebus-bar 30 thus formed has two depressed portions 34 and 36 which makecontact with the front electrode 18.

After the bus-bar 30 has dried, the second protective layer 38 of glassis applied (FIG. 9) over the assembly by the same method and from thesame material as described in connection with the layer 22. However,this layer 38 extends around the underlying layers and forms anoverlapping lip 40 that is bonded to edges of the base electrode 11 (seeFIG. 2) and thus seals off the lamp from the atmosphere. When the secondcover coat 38 has dried, an opening 44 (FIG. 10) is provided thereinthat is aligned with the opening 20 and thus exposes a predeterminedarea of the raised portion 32 of the bus-bar 30. The completed assemblyis then fired at about 650 C. for give minutes to fuse the second covercoat and anchor it in place. The top contact can be made by pressuretechniques or soldering as described above.

EMBODIMENT II In FIGS. ll and 12 there is shown another embodiment ofthe invention wherein elements corresponding to those shown in FIGS.1-10 are'identified by like, primed reference numerals. It will be notedthat the lamp 10 again includes a metal base electrode 11' of stainlesssteel or the like which is coated with a white porcelain enamel layer12. Over the enamel layer 12' in a localized area is an insulating andreinforcing glass layer 14'. Over this reinforcing layer and theremainder of the porelain enamel layer 12' is a phosphor-glass layer 16which, in turn, is coated with a light-transmitting electrode 18'.

In the manufacture of the lamp 10' shown in FIGS. 11 and 12, the glassreinforcing layer 14' is initially applied, followed by the applicationof the glass-phosphor layer 16 in the manner described in connectionwith the embodiment of FIGS. l-l0. In the glass-phosphor layer 16 thereis provided an opening 56 which exposes a rectangular corner-portion ofthe reinforcing glass layer 14', the outline of which is indicated bythe broken line 58 in FIG. 12. This portion is then painted with an oilpaste of clear glass frit which may, for example, be of the samematerial as the cover coats 22 and 38 described in connection with theembodiment of FIG. 2 as well as the cover coat of the presentembodiment, hereinafter described. The clear glass coating in thisregion is applied thicker than the glass-phosphor layer 16' to provide aglass insulating block 60 (FIG. 11). With this construction, it will benoted that a stepped effect is produced between the block 60 and theglass-phosphor layer 16'.

'After drying of the glass material forming the block 60, the coatedsubstrate is fired at 620 C. for five minutes. The frontlight-transmitting electrode 18' is applied as the laminated substrateis withdrawn from the furnace. When cool, the electrode 18 is removedfrom the edges of the substrate and also from the area above the block60.

An elongated bus-bar 30' of burnish silver is then applied over the topof the block 60 and onto the adjacent portion of the front electrode.The bus-bar 30' thus has a raised portion 62 that overlies the block 60,and a depressed portion 64 which makes contact with the transparentelectrode 18', as shown in FIG. 11. After the bus-bar 30' has dried, acover coat 38 of the same material as cover coats 22 and 38 in FIG. 2,is applied over the entire assembly and provided with an overlapping lip40 which seals the entire assembly off from the atmosphere. When thecover coat 38 dries, a small rectangular area is removed to form anaperture 44' and thus provide access to the bus-bar 30'. The lamp isfired at 650 C. for five minutes to fuse the cover coat 38' and completethe fabrication.

The present invention thus provides new and improved electroluminescentlamp structures wherein the difiiculties previously encountered inproviding suitable contact asv semblies are eliminated by effectivelysealing a portion of the contact bus-bar into the lamp structure and byreinforcing the area beneath the bus-bar. Although the invention hasbeen shown in connection with certain specific embodiments, it will bereadily apparent to those skilled in the art that various changes inform and arrangement of parts may be made to suit requirements withoutdeparting from the spirit and scope of the invention.

I claim as my invention:

1. In an electroluminescent device of the type having a base electrodeand a superposed light-transmitting front electrode, a layer ofdielectric material containing an electroluminescent phosphor sandwichedbetween said electrodes and a protective layer of insulatinglight-transmitting material covering said light-transmitting electrode;an improved contact assembly for the light-transmitting electrodecomprising an opening in said light-transmitting electrode and saiddielectric layer containing the electroluminescent material, a body ofelectrical insulating material in said opening, an elongated contactstrip of conductive material having a portion which overlies said bodyof insulating material and another portion which connects with saidlight-transmitting electrode, and an opening in said protective layerexposing a predetermined area of the portion of said contact strip whichoverlies the body of insulating material, the portion of said strip thatconnects with said light-transmitting electrode being covered by andhermetically united to said protective layer so that the stripconstitutes a sealed-in contact for said device.

2. In an electroluminescent device of the type having a base electrodeand a superposed light-transmitting front electrode, a layer ofdielectric material containing an electroluminescent phosphor sandwichedbetween the electrodes and a protective layer of insulatinglight-transmitting material covering said light-transmitting electrode;an improved contact assembly for the light-transmitting electrodecomprising an opening in said light-transmitting electrode and saiddielectric layer containing the electroluminescent material, a firstlayer of electrical insulating material beneath said opening andprojecting above said base electrode, a second layer of electricalinsulating material in said opening and projecting above saidlighttransmittiug electrode, an elongated contact strip of conductivematerial having a first portion which overlies said second layer ofinsulating material and a second portion which connects with saidlight-transmitting electrode and is located beneath and is bonded tosaid protective layer, and an opening in said protective layer exposingat least a part of said first portion of the contact strip.

3. An electroluminescent device comprising a base electrode and asuperposed light-transmitting front electrode, a layer of dielectricmaterial containing an electroluminescent phosphor sandwiched betweensaid electrodes, an opening in said light-transmitting electrode andsaid dielectric layer, a body of electrical insulating material in saidopening and project-ing above said light transmitting electrode, acontact strip of conductive material having a portion which overliessaid body of insulating material and a depressed portion which isconnected to said lighttransmitting electrode, and a protective layer oflighttransmi-tting insulating material covering the entirety of saidlight-transmitting electrode and said contact strip exceptfor apredetermined area of the portion of said strip which overlies said bodyof insulating material and is thus exposed and serves as a contact forsaid device.

4. An electroluminescent device comprising, a base electrode and asuperposed front electrode, said base electrode comprising a metalsubstrate coated on its upper surface with porcelain enamel and saidfront electrode being light-transmitting, .a layer of glass containingan electroluminescent phosphor sandwiched between said electrodes, anopening in said front electrode and said glassphosphor layer, a body ofelectrical insulating material in said opening and projecting above saidfront electrode, a contact strip of conductive material having a portionwhich overlies said body of insulating material and a depressed portionwhich is connected to said front electrode, and a protectivelight-transmitting layer of glass covering the entirety of said frontelectrode and said contact strip except for a predetermined area of theportion of said strip which overlies said body of insulating materialand is left exposed to serve as a contact for said device.

5. The electroluminescent device of claim 4 wherein; the body ofinsulating material beneath the contact strip comprises glass, and thecontact strip is formed from burnish silver.

6. An electroluminescent device comprising a base electrode and asuperposed light-transmitting front electrode, a layer of dielectricmaterial containing an electroluminescent phosphor sandwiched betweensaid electrodes, an opening in said front electrode and saidphosphor-dielectric layer, a first layer of electrical insulatingmaterial.

beneath said opening, a second layer of electrical insulating materialwithin the opening and projecting above said front electrode, a contactstrip of conductive material having a portion which overlies said secondlayer of insulating material and a depressed portion which is connectedto said front electrode, and a protective layer of light-transmittingvitreous material covering the entirety of said front electrode and saidcontact strip except for a predetermined area of the portion of saidstrip which overlies said second layer of insulating material which thusremains exposed and serves as a contact tf'OI' said device.

7. In an electroluminescent device comprising a base electrode and asuperposed front electrode that is lighttransmitting, a layer ofdielectric material containing an electroluminescent phosphor sandwichedbetween said electrodes, an opening in said front electrode and saidphosphor-dielectric layer, a first layer of transparent insulatingmaterial covering said front electrode and extending into said opening,a pair of apertures in said first layer of transparent insulatingmaterial disposed on either side of said opening and exposing said frontelectrode,

a contact strip of conductive material extending over said opening andinto said pair of apertures where they connect with said frontelectrode, and a second layer of transparent insulating materialcovering said first layer and said contact strip except for apredetermined portion of said strip between said pair of apertures, saidpredetermined portion being above the opening in said front electrodeand said phosphor-dielectric layer and comprising an exposed contact forsaid device.

8. An electroluminescent device comprising a base electrode and asuperposed ttront electrode that is lighttransmitting, a layer ofdielectric material containing an electroluminescent phosphor sandwichedbetween said electrodes, a first layer of glass between said baseelectrode and said phosphor-dielectric layer, said first layer coveringonly a localized area of said base electrode, an

opening in said :front electrode and said phosphor-dielectric layer'above said first glass layer, a second layer of glass coveringsubstantially the entirety of said front electrode and extending intosaid opening, a. pair of apertures in the second :layerof glass disposedon either side of said opening and exposing said front electrode, acontact strip of conductive material extending between and into saidpair of apertures and connected to said front electrode, and a thirdlayer of glass covering said second glass layer and said contact stripexcept for a predetermined portion Oif said s t-rip that is locatedbetween said pair of apertures and above said opening and thus comprises"an exposed contact for said device.

9. An electroluminescent device comprising a base electrode and asuperposed front electrode that is lighttransmitting, a layer ofdielectric material containing an electroluminescent phosphor sandwichedbetween the conductive layers, an opening in said front electrode andsaid phosphor-dielectric layer, a block of electrical insulatingmaterial in said opening projecting above the front electrode, a contactstrip of conductive material having a first portion which overlies saidinsulating block and a second depressed portion which connects with saidfront electrode, and a protective layer of transparent insulatingmaterial covering said front electrode and said contact strip in theirentirety except [for a predetermined area of said first portion of thestrip which overlies said insulating block and comprises an exposedcontact for said device.

References Cited by the Examiner UNITED STATES, PATENTS 2,900,271 8/1959Macintyre et al 11733.5 3,109,958 11/1963 De lacha'pelle et al. 313-108X 3,153,167 10/1946 Rulon et al. 313-408 GEORGE N. W ESTBY, PrimaryExaminer.

R. JUDD, Assistant Examiner.

1. IN AN ELECTROLUMINESCENT DEVICE OF THE TYPE HAVING A BASE ELECTRODEAND A SUPERPOSED LIGHT-TRANSMITTING FRONT ELECTRODE, A LAYER OFDIELECTRIC MATERIAL CONTAINING AN ELECTROLUMINESCENT PHOSPHOR SANDWICHEDBETWEEN SAID ELECTRODES AND A PROTECTIVE LAYER OF INSULATINGLIGHT-TRANSMITTING MATERIAL COVERING SAID LIGHT-TRANSMITTING ELECTRODE;AN IMPROVED CONTACT ASSEMBLY FOR THE LIGHT-TRANSMITTING ELECTRODECOMPRISING AN OPENING IN SAID LIGHT-TRANSMITTING ELECTRODE AND SAIDDIELECTRIC LAYER CONTAINING THE ELECTROLUMINESCENT MATERIAL, A BODY OFELECTRICAL INSULATING MATERIAL IN SAID OPENING, AN ELONGATED CONTACTSTRIP OF CONDUCTIVE MATERIAL HAVING A PORTION WHICH OVERLIES SAID BODYOF INSULATING MATERIAL AND ANOTHER PORTION WHICH CONNECTS WITH SAIDLIGHT-TRANSMITTING ELECTRODE, AND AN OPENING IN SAID PROTECTIVE LAYEREXPOSING A PREDETERMINED AREA OF THE PORTION OF SAID CONTACT STRIP WHICHOVERLIES THE BODY OF INSULATING MATERIAL, THE PORTION OF SAID STRIP THATCONNECTS WITH SAID LIGHT-TRANSMITTING ELECTRODE BEING COVERED BY ANDHERMETICALLY UNITED TO SAID PROTECTIVE LAYER SO THAT THE STRIPCONSTITUTES A SEALED-IN CONTACT FOR SAID DEVICE.